<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<script src="http://code.jquery.com/jquery-latest.js"></script>
<script>
var sum = 0;
$(document).ready(function() {
  $('[name="num"]').on('click', getSum);
 });
 
 function getSum() {

  var $isChecked = $(this).prop('checked');
  
  if($isChecked) {
   sum += parseInt($(this).val()); 
  } else {
	  sum -= parseInt($(this).val());
  }
  
  $('#sum').text(sum);
 }
</script>
<title>Insert title here</title>
</head>
<body>

 <div>
  <span>
   점수 1 : <input type="checkbox" name="num" id="1st" value="10" />
  </span>
  <span>
   점수 2 : <input type="checkbox" name="num" id="2nd" value="30" />
  </span>
  <span>
   점수 3 : <input type="checkbox" name="num" id="3rd" value="50" />
  </span>
 </div>
 <div id="sum"></div>

</body>
</html>